Field of the Invention
The present invention relates to novel .alpha.-hydroxylated .beta.-unsaturated carboxylic acids. In more detail, it relates to novel .alpha.-hydroxy-acids of the general formula: ##STR2## The present invention also relates to the process of preparation and to the use of .alpha.-hydroxy-acids of formula (I). In particular, these novel products represent intermediates which provide access, by oxidative decarboxylation, to homologous lower aldehydes (prenal, citral, etc.). Such aldehydes in turn allow access to vitamin A or can also be used for their aroma properties.
It is known from French Patent 1,554,805 to prepare .alpha.-ethylenic carbonyl compounds by isomerization of .alpha.-acetylenic alcohols. This isomerization takes place by heating the alcohol, optionally in a solvent, in the presence of small quantities of a catalyst based on a metal belonging to groups 3b to 7b of the periodic table of the elements Advantageously, this isomerization takes place in the liquid phase, and the catalyst is an inorganic or organic derivative of a metal selected from the group comprising vanadium, niobium, molybdenum, tungsten and rhenium.
It is also known from U.S. Pat. No. 3,057,888 to prepare unsaturated aldehydes from esters of 1,1-disubstituted propargyl alcohol by heating in an acidic medium in the presence of a catalyst containing a metal belonging to group lb of the periodic table of the elements.
Moreover, it is known from U.S. Pat. Nos. 2,524,865 and 2,524,866 to prepare ethylenic aldehydes by treating alkynols in the vapour phase under the action of various acidic catalysts. However, this process gives only a ternary mixture of an ethylenic aldehyde, ketone and hydrocarbon.
The present invention describes a novel access route to these aldehydes, and in particular to prenal and citral, from esters of .beta.,.gamma.-unsaturated carboxylic acids. In addition, this route gives very good yields and has made it possible to display and to isolate novel .alpha.-hydroxylated .beta.-unsaturated carboxylic acid compounds as intermediates.